Our research will continue to use a multidisciplinary approach to establish neurophysiological, neuroanatomical, and neurobehavioral markers that differentiate autism from other developmental disorders of communication. (1) Neurophysiological markers will continue to be established by the identification of aberrant sensory and cognitive ERPs in autism and developmental dysphasia. We will determine whether neurophysiological abnormalities in autism occur predominantly in attentional and cognitive, as opposed to sensory, ERPs; whereas in dysphasia, neurophysiological abnormalities occur throughout sensory and cognitive stages of auditory, but not in visual and somatosensory, information processing. (2) Neuroanatomical markers will continue to be established by identifying abnormal neuroanatomical structures using MRI (magnetic resonance imaging) technology. In particular, we will determine whether the distinctive hypoplasia of the cerebellar vermis, which we have found in several non-retarded autistic people, is also present in retarded autistic people, but not in dysphasic and mentally retarded non-autistic people. (3) Neurobehavioral markers will be sought by evaluating the long-term habituation of the acoustic startle response, a potentially distinctive neurobehavioral marker which, heretofore, has not been fully researched in autism. Recent basic research with animals shows that the cerebellar vermis is central to systems which mediate one form of memory -- the long-term habitation of the acoustic startle response. Since our preliminary MRI data has shown that this neuroanatomical structure is abnormal in some autistic people, we will determine whether autistic people have a deficit in the long-term habituation of this response. Neurologic symptoms and signs of cerebellar disorder, such as dysarthria and nystagmus, will be clinically evaluated.